Recent years have seen the rapid growth of the Internet. Many developments have come together to produce the Internet that we know today, and one of them is the use of applets, written in languages such as Java, which are executable programs that can be run by a web browser. In addition, faster modems have led to shorter downloading times. This has led to a growth in the downloading of programs in general directly from the Internet. The Internet is eminently suitable for such use, and one of the reasons why such use is not widespread is that people are afraid to use the Internet. This is for two main reasons. The first is that they are afraid of downloading software whose behavior is not known or that may contain viruses. The second is that they are afraid that confidential information, such as credit card numbers and the like, may somehow be made available to parties other than the intended recipients.
In regard to viruses, programs have been around for many years that detect the presence of viruses, and either delete the viruses themselves, or delete the infected file. These programs depend on recognizing specific virus programs or on recognizing strings of program code that look as though they might have the potential to carry out activities normally associated with viruses. In order to overcome the virus detection programs more recent viruses have been designed to introduce chances to themselves when they replicate so that they do not fit in with any template or pattern that the virus detector might be using. Furthermore a virus detection program has only a limited chance, of detecting a virus that was not know about when the detection program was written, especially if the way in which the virus was written is radically different from previous viruses, as occasionally happens. Furthermore virus detection programs are generally ineffective at detecting viruses that are written as macros within programs.
In any case it cannot be guaranteed that conventional countermeasures will work against all viruses, and the fear of computer viruses has been a serious impediment to the development of the Internet.
Virus detection programs also cannot detect what are known as “vandals”. “Vandals” differ from viruses in that they are complete programs that are executable in themselves, as opposed to viruses, which cannot work by themselves and need to infect host programs in order to be able to replicate and cause damage. Vandals are programs that carry out activities outside the range of expectations of the user. For example they may damage or delete other files or interfere with the operation of other programs. Internet style applets make ideal vandals as they can often be downloaded from the internet through one's web browser without the user even being aware of its a presence.
The theft of confidential information is another task that vandals can carry out. The vandal applet is downloaded from the internet without the knowledge of the user and begins to scan the disk for the confidential information, or wait for the user to enter such information for some other purpose. It then passes the information to a specific site at some time that the user is connected to the Internet, again without the user being aware that anything untoward has occurred.
The reason that anti-virus programs have difficulty in detecting vandal programs is that they are not viruses and indeed lack many of the fundamental features of viruses, that is to say they do not replicate and they do not modify existing files as they infect them. Furthermore the preparation of a reliable anti-vandal program is problematic because it is difficult to lay down precise criteria to enable a computer program to distinguish between a wanted applet and a vandal.